A short while ago, they banned all fluids, of any kind, including bottled water, on commercial passenger flights, here in the USA. I think this was relaxed just a little...lipstick was allowed, and I suppose ChapStick. Otherwise, I haven't heard of much else being allowed. I suspect most countries would have a much more relaxed attitude than here, so you might be ok from Ozzie.
The reasoning behind the fluids ban, was that some fluids are dangerous, and it's easier to ban all fluids than it is to train their minimum wage security guards to look for the dangerous ones. Pretty hard to argue with the logic, considering how few HS students take Chemistry these days.
Castor oil would be an ORM-D (I think) item, meaning that if it leaks, it will be messy, but not dangerous, so you should be able to mail order it from SIG or the fuel guys in Oz (Magnum?). Synthetic oil would be a little more questionable, I think, because it probably will be listed as flamable. Regarding alcohol, you don't need a super pure grade. Shellac thinner should do just fine, if it hasn't absorbed too much of the local humidity. If it doesn't work fine, dump it into the petrol tank of the Land Cruiser.
If I was in PNG, I would search out engines that are made to run on straight alky and oil. Stalkers come to mind, and they're available from Kaz Minato in Japan, tho made in Russia or Ukraine. Possibly that could be a business trip deal. Let us know if you need contact information.
Steve